Devices, systems and methods for controlling local blood pressure

ABSTRACT

Devices, systems, and methods for controlling local blood pressure. In an exemplary embodiment of a device for exposing a blood vessel to increased pressure of the present disclosure, the device comprises an anchor configured for placement into a blood vessel and to expand independently from a particle held from flowing away by the anchor, the particle configured to gradually expand due to exposure to blood flow.

RELATED APPLICATIONS

The present application is related to, claims the priority benefit of,and is a U.S. continuation application of, U.S. Nonprovisional patentapplication Ser. No. 11/720,224, filed on May 25, 2007 and issued asU.S. Pat. No. 8,361,101 on Jan. 29, 2013, which is related to, claimsthe priority benefit of, and is a U.S. national stage patent applicationof, PCT Patent Application Serial No. PCT/US2005/042911, filed on Nov.28, 2005, which is related to, and claims the priority benefit of, U.S.Provisional Patent Application Ser. No. 60/630,563, filed Nov. 26, 2004.The contents of each of these applications are hereby incorporated byreference in their entirety into this disclosure.

BACKGROUND

The present disclosure relates to controlling blood pressure, including,but not limited to, devices, systems and methods for controlling bloodpressure in vessels in vivo to change the physiology of such bloodvessels.

An area of surgical medicine where the health and well-being of apatient have not progressed as well as the commonplace nature of thesurgery is replacement of arteries due to damaged or diseased state.Although the option of introducing an artificial blood vessel has beenused successfully for years, because of the inherent problems ofbiocompatibility and the resultant chance of implant rejection by thebody as well as clotting and other factors, it is often most ideal touse a patient's own blood vessels when there is a need to substitute fora diseased or damaged vessel.

In such a procedure, when a patient's artery needs to be replaced with asubstitute, a surgeon picks one of the patient's veins to serve as thesubstitute, thereby essentially avoiding any complications relating tobiocompatibility. However, because the architecture of the veins tendsto be significantly different than the artery that they were intended toreplace, the transposed vein typically is exposed to conditions forwhich it is not designed, resulting in structural or physiologicaldamage to the vein. One of the most significant factors that contributeto the failure of the vein in its new location is directly attributableto the significantly increased blood pressure inherent in the arterialsystem as opposed to the venous system.

Thus, a need exists in the art for an alternative to the conventionalmethods of replacing damaged or diseased arteries with veins from thesame patient that allows the vein to better handle its new function andposition but without the drawbacks of conventional methods, whichinclude repeated care or operations or the inherent shock to the venoussystem from the shock of sudden exposure to arterial pressure.

SUMMARY

The present disclosure provides an alternative and enhancement toconventional treatments for artery disease as well as other blood vesselconditions where the artery needs to be corrected through conventionalmethods, such as balloon catheter enlargement, or altogether replacedwith another blood vessel, either artificial or natural. The presentdisclosure uses the findings that occluded blood vessels cause anincrease in interior blood pressure, thereby allowing a thickening ofthe vessel wall, or “arterialization.” Through use of unique devices,systems and methods, the present disclosure induces an arterializationof a desired section of the venous system through a gradual andminimally-shocking manner so that the venous system is conditioned toaccept an increase in blood pressure, thereby making any eventual toincreased blood pressure much less traumatic than conventional methods.

In exemplary embodiments, the present disclosure makes use of enclosuresin blood vessels that enclose particles which increase in size, therebyresulting in an increased occlusion for the blood vessel, and resultantincrease in pressure to the exposed blood vessels. This arterializationof the blood vessels conditions them for eventual increases in bloodpressure so that they are better able to handle their new location whenthey are transposed to an arterial position within the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of the relation of blood flow (upper curves) andpressure (lower curves) with respect to changes in cross-sectionalocclusion, as through a stenosis.

FIG. 2 shows an exemplary embodiment of the present disclosure as beingintroduced into a blood vessel through a conventional balloon catheter.

FIG. 3 shows a technique according to an exemplary embodiment of thepresent disclosure of arterializing a vein to prepare it for eventualrelocation to an arterial position using an enclosure that serves toincrease the pressure exposed on the interior of the vein.

FIG. 4 shows a technique according to an exemplary embodiment of thepresent disclosure of arterializing a vein to prepare it for eventualrelocation to an arterial position using an externally-controlledintravascular balloon that serves to increase the pressure exposed onthe interior of the vein.

FIG. 5 shows a schematic diagram of a system according to the presentdisclosure and shown in FIG. 4 having internal and external componentsworking in unison to control the intravascular pressure within a bloodvessel.

DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of this disclosure is thereby intended.

The present disclosure provides systems and methods for addressing someof the problems associated with conventional methods of replacingarteries with veins. The problems that are common in such operationsinclude the need for repeated operations, the relatively high level offurther medical conditions or mortality resulting from the shock of thevenous system to arterial pressure, and other drawbacks known to onehaving ordinary skill in the art.

The present disclosure takes advantage of the findings of studies, shownin FIG. 1, that teach that blood flow remains mostly constant in a bloodvessel as the cross sectional area decreases until a critical stenosisis reached. In other words, pressure increases steadily while the flowremains relatively constant until the critical stenosis point. Prior toabout 80% stenosis, the increase in pressure is much more significantthan the drop in blood flow. However, after the cross sectional area ofan occluded blood vessel becomes about 20% of the original non-occludedcross-section of the vessel, internal blood pressure increases in asteady manner. As shown in FIG. 1, internal vessel pressure risesrapidly when the cross-sectional area of the blood vessel falls to 20%of original area and below. This may be explained by the naturaldistensibility and flexibility of the blood vessel to account for somenatural occlusion. However, at about the threshold of 20%, the bloodvessel loses its ability to account for any occlusion, and pressureincreases rapidly while the blood flow decreases in an inversely similarmanner. A conclusion that may be made is that patients who have bloodvessels with some occlusion may not immediately sense the effects ofsuch occlusion until the occlusion takes up some 80% of thecross-sectional area of a normal non-occluded blood vessel.

Studies have shown that blood vessels, particularly veins, have theability to transform themselves into arterial-like vessels when anoutside stimulus (for example, higher blood pressure) is imposed uponthem. Using this finding, any attempt at transforming a vein into anarterial-like blood vessel through an increase in blood pressure broughtabout by vessel occlusion would necessarily require a stenosis thatresults in at least a 80% blockage of the natural cross-sectional areaof the normal blood vessel. Stated differently, a stenosis would have toresult in a cross-sectional area of about 20% of the originalcross-sectional area of the blood vessel in order to begin to produce anincrease in blood pressure that would result in the physiologicalchanges necessary to transform a vein into an arterial-like vessel.Although the statements made here with respect to FIG. 1 refer to 80%occlusion and its corresponding cross-sectional area of 20%, such valuesare merely exemplary and dependent on the particular organ and samplebeing considered in FIG. 1. More representative values for specificorgans or systems are dependent on those systems. The main teaching,however, is that pressure drops more rapidly than flow at a criticalstenosis point as a blood vessel is increasingly occluded.

A rapid attempt at the transformation of a vein into pan arterial-likevessel results in damage to the venous wall because of the shock of thestep-like increase in blood pressure. In cases where a vein, withinternal blood pressure in mmHg in the low teens to single digits israpidly or in a step-like manner exposed to an arterial blood pressure,which is about an order of magnitude greater, the blood vessel attemptsthe process of physiological transformation to an arterial-like vesselquickly. However, the order of magnitude increase in pressure does notallow the architecture of the blood vessel to transform smoothly and inan orderly fashion, and deterioration of the blood vessel wall and othersimilar damage are not uncommon.

Part of the basis for the devices, systems and methods according to thepresent disclosure is to take advantage of the findings that bloodvessels do have the ability to change from one form to another dependingon the type of pressure to which they are exposed. However, the presentdisclosure also attempts to at least minimize if not eliminate theproblems and drawbacks with conventional step- or rapid-exposure methodsof exposing a vein to arterial pressure by creating a graded orgradual-increase in pressure to the vein.

Thus, systems and methods according to the present disclosure create aninternal environment for the vein that results in a gradual increase andexposure to the levels of arterial blood pressure such that any risks ofshock or disintegration of the blood vessel wall because of conventionalexposure to a step-increase in blood pressure is minimized or avoided.Thus, various devices, systems and methods are introduced herein thathave the ability to create a gradual increase in blood pressure withinpre-determined areas of a blood vessel while maintaining relativelyconstant blood flow through the vessel. Although certain exemplaryembodiments of the disclosure are shown, the disclosure is not limitedto these mere examples, and has a scope beyond the examples shownherein, to all devices, systems and methods that have the capability ofproducing a graded increase in blood pressure within the interior of ablood vessel, resulting in a gradual transformation of blood vessel wallthickness from that of vein or venule to a more arterial-like vessel, sothat such venous blood vessels are better prepared to handle thepressures of their new position on the arterial side aftertransplantation.

In an exemplary embodiment of the present disclosure, as shown in FIG.2, a conventional balloon catheter 10 is used to enter a blood vessel20. Such procedures are conventionally performed to increase thecross-sectional area of an at least partially occluded blood vessel,such as an artery. As used here, the same conventional method ofinserting a balloon catheter inside a blood vessel is used to initiallyintroduce the balloon catheter into a predetermined section of a desiredblood vessel that needs to be conditioned for eventual transplantationto another part of a patient's body. Once in place, the balloon isenlarged through conventional procedures. On the exterior of the balloonis a mesh-like enclosure that conforms to the contour of the balloon.

After the balloon is enlarged, the mesh-like enclosure (anchor orenclosure 40) is relatively anchored in place within the blood vessel(in lumen 50) by friction fit of its exterior points with the interiorof the blood vessel wall. The balloon is typically then deflated andremoved. However, the enclosure is then left in place, having beenlocked into place within the blood vessel.

Although such mesh-like enclosures may resemble conventional devicessuch as stents, the enclosure as described herein has a geometry that isdistinguishable from conventional stents. As seen in the schematic crosssectional view in FIG. 2, the outer ends of the enclosure have anexterior wall that is used to create a cage-like environment within theinterior space of the mesh-like enclosure. This cross-sectional view ofthe end walls is not drawn to scale but is enlarged to highlight itsgeometry. This architecture is unique and distinct from conventionalstents, which typically attempt to maintain or enlarge the structuralgeometry of a portion of a blood vessel while, at the same time, nothindering blood flow therethrough by introducing anything thatencroaches into the cross-sectional area of the blood vessel. In fact,the very purpose of many stents is to enlarge the blood vesselcross-sectional area, and not to impose upon it in any way.

As shown in FIG. 2 and described herein, and in contrast withconventional stents, the cage-like enclosure 40 that is created serves apurpose to act as a trap or guard to the movement of a particle 60,which is either trapped within the cage or is beyond the end walls ofthe cage or some combination thereof. Such geometry serves in theoverall process of introducing a graded pressure increase environment,as described further herein.

Once the cage-like enclosure has been created, a particle may beintroduced into its interior. This interior particle has a uniqueproperty of being expandable with increased exposure to the interiorblood vessel environment. For example, it may be an object that retainsfluids from the blood vessel when exposed thereto, or in response to achemical introduced thereto.

In the exemplary embodiment shown in FIG. 2, the interior particle is apill, made primarily of ameroid, a dehydrated protein structure.However, the present disclosure is not limited to pill shapes orameroids or the combination. Any material of any shape may be used thatis introducible to the blood vessel environment, does not createphysiological harm, and is capable enlarging in time. Other shapes, suchas masses (e.g., conventional children's play putty), or othermaterials, such as biocompatible polymers (e.g., hydrophilic polymerscapable of attracting water) may also be used. One of ordinary skill inthe art would be cognizant of other shapes and materials that may beused in the disclosure described herein, and all such other shapes andmaterials, although not described specifically herein for sake ofbrevity, are within the scope of the present disclosure.

As shown in the example of FIG. 2, an ameroid pill is introduced intothe enclosure by the lumen of the catheter. The ameroid pill isinitially dry as it is inserted into the enclosure. Once in theenclosure, the pill is exposed to the surrounding environment of theblood vessel, thereby gaining moisture and enlarging in reactiontherewith. This gradual attraction of fluid and enlargement of theameroid pill contributes to the gradual increase in girth and overallsize of the ameroid pill. As blood continually flows through the bloodvessel, as shown in FIG. 2, the ameroid pill enlarges within itsconfined area and continues to create a gradual decrease incross-sectional area of the blood vessel. As shown in FIG. 1, once thecross-sectional area of a blood vessel is such that it is about 20% ofthe original area, then blood flow decreases somewhat while bloodpressure increases noticeably, which results in physiological changes inthe blood vessel walls which are exposed to this increase in bloodpressure.

Use of the concept exemplified in FIG. 2 results in gradual conditioningof a blood vessel to increased levels of pressure such that itsphysiological changes in geometry are gradual, and not shockingly rapid.This will serve to decrease or prevent any of the conventional drawbacksof conventional methods where certain blood vessels, such as veins, areexposed to arterial blood pressures in a shocking step-like manner,resulting in high rates of eventual failure or vessel structurebreakdowns.

In use, the concept shown in FIG. 2 may be used to assist in theimproved conditioning of veins before they are introduced into locationswhere they serve as arteries. In the non-limiting example shown in FIG.3, a device according to the present disclosure is introduced into atarget vein, such as the femoral or saphenous vein, commonly used toreplace diseased or damaged arteries in coronary artery bypass.

As shown in the two exemplary steps of FIG. 3, a device according to thepresent disclosure is introduced into the interior of the femoral veinthrough conventional methods, such as the catheter method described withrespect to FIG. 2. Once in place, the enclosure device allows exposureof the ameroid pill contained therein to the flow of blood traversingthrough the blood vessel. With time, the ameroid pill retains moisturefrom the flowing blood and increases in girth and size. As the ameroidpill increases in size, its overall volume serves to decrease thecross-sectional size of the blood vessel in which the enclosure ispositioned. As shown in the graph of FIG. 1, with an increase incross-sectional area occlusion, an increase in blood pressure occurs,particularly beyond a certain level of occlusion, as shown in FIG. 1.Thus, as the ameroid pill increases in size, the part of the femoralvein that is upstream of the enclosure increases in size as itarterializes in response to the increase in pressure. At some point intime, the ameroid pill is enlarged to a point that it serves tosignificantly decrease, but not altogether stop, the blood flow throughthe femoral vein, as shown in the second diagram of FIG. 3. Althoughsuch decreased blood flow and near complete occlusion would createtissue hypoxia and eventual death if occurring on the arterial side, thehighly vascular nature of the venous system allows for redundant flowsto account for any such induced or natural vessel blockage. Furthermore,the time required to create such blockage is determinable by a healthcare professional as a function of the size of the blood vessel areabeing blocked as well as the size of the ameroid pill and the absorbencyqualities of such a pill. Such factors would be known to one havingordinary skill in the art without the need for undue experimentation.For example, in pig studies, it has been found that a two week period issufficient for arteralization of veins.

Further, the shape of the ameroid may be any that functions according tothe description presented herein. A particular embodiment of the ameroidpill, as shown in exemplary embodiments, is in the configuration of abullet, with transitionally tapered ends, thus enabling less hemodynamicflow disturbances and greater streamlined flow.

When it has been determined that the time of exposure of the femoralvein to a low-flow condition has been sufficient to initiallyarterialize the blood vessel in a healthy manner, a surgeon can thenintroduce an induced occlusion in an upstream location with respect tothe implanted enclosure, as shown in the second diagram of FIG. 3.Furthermore, an A-V fistula with a stent is created in position on thefemoral vein somewhere between the induced occlusion upstream thereto,and the enclosure with particle downstream thereto, such that femoralartery blood flows into the femoral vein and is directed through thereduced flow enclosure located downstream. The femoral vein, having beenexposed to a reduced flow (and increased pressure) environment for atime period that allowed it to arterialize by thickening its walls, isnow not as “shocked” by its sudden exposure to femoral artery pressurethrough the fistula.

Thus, at the least, the femoral vein would be exposed to one muchsmaller step increase in pressure using the teachings of the presentdisclosure, as opposed to one very large increase in blood pressureexposure. In essence, blood vessels that have undergone the methodstaught by the present disclosure are exposed to a gradual increase inpressure to a given high point for the femoral vein, at which time, theyare then introduced to a higher pressure level (when A-V fistulacreated), where the higher pressure level is not as high a step increaseas it would be using conventional surgical methods.

As determined by a surgeon, the time exposure of a patient to thecondition shown in the second diagram of FIG. 3 would be dependent onvarious factors, including the level of further arterialization needed,the type of particle being used, as well as other factors known to onehaving ordinary skill in the art. When the desired time is reached, thesurgeon can then safely close off the fistula as well as positions atthe upstream induced occlusion sight and the downstream enclosure sight,and remove the portion of the femoral vein positioned therebetween,which has been exposed to higher blood pressures from the femoral arteryand conditioned to better accept its position in the arterial side ofthe circulatory system. The thickened wall portion of the femoral veinis then transplanted into its new pre-designated higher pressurelocation for which it has been conditioned to withstand. This decreasesany eventual shock that the femoral vein would have been exposed to hadit not been pre-conditioned for the additional pressure.

Although the examples above have shown the ameroid pill (a particle 60)being located inside of the cage-like enclosure, the present disclosureis not limited to such an architecture, nor are other alternatives notpossible. For example, the ameroid pill may be positioned outside of thecage-like enclosure and attached thereto through an attaching medium 70such that the increased size and girth of the pill serves to decreasethe flow of blood past the enclosure.

In another exemplary embodiment of the present disclosure shown in FIGS.4 and 5, an alternative approach is taken in arterializing a vein whichintroduces a balloon catheter into the a-v fistula. In this exemplaryembodiment, the ameroid pill and surrounding cage is replaced by a morecontrolled system. A balloon is introduced into the femoral vein, in asimilar geometry as that shown with respect to FIG. 3. However, as shownin FIG. 4, the balloon is positioned on tubing that has sensorspositioned in a more distal position thereon. Such sensors couldinclude, for example, a flow sensor and a pressure sensor. Other sensorsare also possible and apparent to one having ordinary skill in the art.

Proximal to the balloon is tubing that leads to outside of the body andinto an externally located micro pump. This pump is used to control thesize of the balloon which is positioned inside of the femoral vein. Inuse, the pressure and flow are continuously sensed and the balloonvolume is adjusted to increase the pressure at the desired rate. Controland feedback circuitry is needed to allow for proper inflation of theballoon. Such control mechanism includes, for example, DC conditions andamplifier, analog input and output board, and a software controller,which includes a data acquisition system, a feedback signal sensor, anda command signal generator.

In use, the sensors (e.g., flow, pressure) located within theintravascular space, send signals to the DC condition and amplifierthrough hard wire and/or wireless transmission, wherein such signals arethen forwarded to the analog input/outboard. There it is incommunication with the software controller, which then, depending on themeasured flow and/or pressure, transmits a command back to the outputboard which then directs a change in the external pump, directlyaffecting the size of the balloon inside of the vascular space.

This dynamic controller system, shown in FIGS. 4 and 5, allows forfeedback control of the rate of pressure change. For example, if theinternal blood pressure is too low, the feedback system loop allows foran inflation of the balloon resulting in increased blood pressure.Alternatively, if the blood pressure is too high, the feedback loopallows for a deflation of the balloon resulting in decreased bloodpressure. Although the sensors, balloon, and other individual componentsused in the present embodiments may be apparent to one having ordinaryskill in the art, the system as a whole and the manner of use resultingin a feedback controlled blood pressure controller, is novel andnon-obvious and presents a significant advantage over other conventionaltechniques in use today. Further, the position of the sensors may beinterchanged as needed without departing from the disclosure.

As shown in the block diagram of the set-up in FIG. 5, the externalportion of the system may be placed in a small jacket strapped to theleg of the patient for the period (e.g., two weeks) of thearterialization. Other positions and configurations are also possibleand within the scope of the present disclosure. After a vein isarterialized using the technique shown here, the patient is ready forsurgery. At the time of surgery, the arterialized vein would beharvested and the balloon catheter removed.

While various embodiments of devices and systems of controlling localblood pressure and methods of using the same have been described inconsiderable detail herein, the embodiments are merely offered asnon-limiting examples of the disclosure described herein. It willtherefore be understood that various changes and modifications may bemade, and equivalents may be substituted for elements thereof, withoutdeparting from the scope of the present disclosure. The presentdisclosure is not intended to be exhaustive or limiting with respect tothe content thereof.

Further, in describing representative embodiments, the presentdisclosure may have presented a method and/or a process as a particularsequence of steps. However, to the extent that the method or processdoes not rely on the particular order of steps set forth therein, themethod or process should not be limited to the particular sequence ofsteps described, as other sequences of steps may be possible. Therefore,the particular order of the steps disclosed herein should not beconstrued as limitations of the present disclosure. In addition,disclosure directed to a method and/or process should not be limited tothe performance of their steps in the order written. Such sequences maybe varied and still remain within the scope of the present disclosure.

What is claimed is:
 1. A device for exposing a blood vessel to increasedpressure, the device comprising: an anchor configured for placement intoa blood vessel along with a particle and to expand independently fromthe particle; and the particle, which is held from flowing away by theanchor, configured to gradually expand due to exposure to blood flowwithin the blood vessel and configured to decrease a cross-sectionalarea of a lumen of the blood vessel exposed to the blood flow inside theanchor, resulting in a decrease in blood flow and an increase in bloodpressure inside the anchor.
 2. The device of claim 1, wherein the anchoris further configured for delivery into the blood vessel by way of aballoon catheter.
 3. The device of claim 2, wherein the anchor isfurther configured for placement around an outer circumference of aballoon of the balloon catheter.
 4. The device of claim 3, wherein whenthe balloon is inflated and the anchor is placed around the outercircumference of the balloon, the anchor expands due to inflation of theballoon.
 5. The device of claim 1, wherein the particle comprises anameroid pill.
 6. The device of claim 1, wherein the particle ispositioned within the anchor.
 7. The device of claim 1, wherein theparticle is coupled to but disposed outside of the anchor.
 8. The deviceof claim 1, wherein the anchor is configured to span across across-sectional area of a lumen of the blood vessel.
 9. The device ofclaim 1, wherein the particle is held from flowing away by the anchor ina direction of the blood flow within a lumen of the blood vessel. 10.The device of claim 1, wherein the particle is inside the anchor.
 11. Asystem for exposing a blood vessel to increased pressure, the systemcomprising: an elongated catheter having a balloon coupled thereto; andan anchor configured for placement into a blood vessel along with aparticle and to expand due to inflation of the balloon and independentlyfrom the particle; and the particle, which is held from flowing away bythe anchor, configured to gradually expand due to exposure to blood flowwithin the blood vessel and configured to decrease a cross-sectionalarea of a lumen of the blood vessel exposed to the blood flow, resultingin a decrease in blood flow and an increase in blood pressure inside theanchor.
 12. The system of claim 11, wherein the anchor is configured toexpand due to inflation of the balloon when the anchor is positionedaround an outer circumference of the balloon.
 13. The system of claim11, wherein the particle comprises an ameroid pill.
 14. The system ofclaim 11, wherein the anchor is configured to span across across-sectional area of a lumen of the blood vessel.
 15. The system ofclaim 11, wherein the particle is held from flowing away by the anchorin a direction of the blood flow within a lumen of the blood vessel. 16.The system of claim 11, wherein when the particle gradually expands dueto exposure to the blood flow, the cross-sectional area of the lumenthat is exposed to the blood flow is decreased, resulting in a decreasein the blood flow.
 17. A method for exposing a blood pressure toincreased pressure, the method comprising: positioning an anchor havinga particle held from flowing away by the anchor into a lumen of a bloodvessel using a balloon catheter, the particle configured to graduallyexpand due to exposure to blood flow within the blood vessel andconfigured to decrease a cross-sectional area of a lumen of the bloodvessel exposed to the blood flow upon expansion; inflating a balloon ofthe balloon catheter to expand the anchor in the lumen, wherein theanchor is expanded independently of the particle; wherein the particledecreases the cross-sectional area of the lumen inside the anchor as itgradually expands due to exposure to blood flow within the lumen,resulting in decreased blood flow and increased blood pressure insidethe anchor at a location of the particle.
 18. The method of claim 17,wherein the positioning step is performed to position the anchor and theparticle within the lumen simultaneously.
 19. The method of claim 17,wherein the positioning step comprises the steps of first placing theanchor within the lumen and subsequently placing the particle within theanchor.
 20. The method of claim 17, wherein the positioning stepcomprises the steps of first placing the anchor within the lumen andsubsequently coupling the particle to the anchor but outside of theanchor within the lumen.